Buggy code:
private , int len ) { } public static String substringBefore ( String str , String separator ) { } public static String substringAfter ( String str , String separator ) { } public static String substringBeforeLast ( String str , String separator ) { } public static String substringAfterLast ( String str , String separator ) { } public static String substringBetween ( String str , String tag ) { } public static String substringBetween ( String str , String open , String close ) { } public static String [ ] substringsBetween ( String str , String open , String close ) { } public static String [ ] split ( String str ) { } public static String [ ] split ( String str , char separatorChar ) { } public static String [ ] split ( String str , String separatorChars ) { } public static String [ ] split ( String str , String separatorChars , int max ) { } public static String [ ] splitByWholeSeparator ( String str , String separator ) { } public static String [ ] splitByWholeSeparator ( String str , String separator , int max ) { } public static String [ ] splitByWholeSeparatorPreserveAllTokens ( String str , String separator ) { } public static String [ ] splitByWholeSeparatorPreserveAllTokens ( String str , String separator , int max ) { } private static String [ ] splitByWholeSeparatorWorker ( String str , String separator , int max , boolean preserveAllTokens ) { } public static String [ ] splitPreserveAllTokens ( String str ) { } public static String [ ] splitPreserveAllTokens ( String str , char separatorChar ) { } private static String [ ] splitWorker ( String str , char separatorChar , boolean preserveAllTokens ) { } public static String [ ] splitPreserveAllTokens ( String str , String separatorChars ) { } public static String [ ] splitPreserveAllTokens ( String str , String separatorChars , int max ) { } private static String [ ] splitWorker ( String str , String separatorChars , int max , boolean preserveAllTokens ) { } public static String [ ] splitByCharacterType ( String str ) { } public static String [ ] splitByCharacterTypeCamelCase ( String str ) { } private static String [ ] splitByCharacterType ( String str , boolean camelCase ) { } public static < T > String join ( T ... elements ) { } public static String join ( Object [ ] array , char separator ) { } public static String join ( Object [ ] array , char separator , int startIndex , int endIndex ) { } public static String join ( Object [ ] array , String separator ) { } public static String join ( Object [ ] array , String separator , int startIndex , int endIndex ) { } public static String join ( Iterator < ? > iterator , char separator ) { } public static String join ( Iterator < ? > iterator , String separator ) { } public static String join ( Iterable < ? > iterable , char separator ) { } public static String join ( Iterable < ? > iterable , String separator ) { } public static String deleteWhitespace ( String str ) { } public static String removeStart ( String str , String remove ) { } public static String removeStartIgnoreCase ( String str , String remove ) { } public static String removeEnd ( String str , String remove ) { } public static String removeEndIgnoreCase ( String str , String remove ) { } public static String remove ( String str , String remove ) { } public static String remove ( String str , char remove ) { } public static String replaceOnce ( String text , String searchString , String replacement ) { } public static String replace ( String text , String searchString , String replacement ) { } public static String replace ( String text , String searchString , String replacement , int max ) { } public static String replaceEach ( String text , String [ ] searchList , String [ ] replacementList ) { } public static String replaceEachRepeatedly ( String text , String [ ] searchList , String [ ] replacementList ) { } private static String replaceEach ( String text , String [ ] searchList , String [ ] replacementList , boolean repeat , int timeToLive ) { } public static String replaceChars ( String str , char searchChar , char replaceChar ) { } public static String replaceChars ( String str , String searchChars , String replaceChars ) { } public static String overlay ( String str , String overlay , int start , int end ) { } public static String chomp ( String str ) { } public static String chomp ( String str , String separator ) { } public static String chop ( String str ) { } public static String repeat ( String str , int repeat ) { } public static String repeat ( String str , String separator , int repeat ) { } public static String repeat ( char ch , int repeat ) { } public static String rightPad ( String str , int size ) { } public static String rightPad ( String str , int size , char padChar ) { } public static String rightPad ( String str , int size , String padStr ) { } public static String leftPad ( String str , int size ) { } public static String leftPad ( String str , int size , char padChar ) { } public static String leftPad ( String str , int size , String padStr ) { } public static int length ( CharSequence cs ) { } public static String center ( String str , int size ) { } public static String center ( String str , int size , char padChar ) { } public static String center ( String str , int size , String padStr ) { } public static String upperCase ( String str ) { } public static String upperCase ( String str , Locale locale ) { } public static String lowerCase ( String str ) { } public static String lowerCase ( String str , Locale locale ) { } public static String capitalize ( String str ) { } public static String uncapitalize ( String str ) { } public static String swapCase ( String str ) { <START_BUG> if ( ( str == null ) || ( ( str . length ( ) ) == 0 ) ) { <END_BUG>

Fix:
if ( StringUtils . isEmpty ( str ) ) {